Biologists increasingly believe we're witnessing the onset of a mass extinction event,
in which the majority of the planet's species may disappear. This latest mass extinction differs from the Earth's previous five such events, they point out, in that we are causing it. But perhaps by studying past mass extinctions, we can learn something about where our current actions may take us. A recent colloquium, "The Future of Evolution," sponsored by the U.S. National Academy of Sciences addressed the science behind the ultimate conservation issue - the fate of the planet's biota - and further, asked whether today's extinction event might mean not only the loss of species and the degradation of ecosystems, but the breakdown of evolutionary processes themselves.
|Are we on the verge of a mass extinction?
Few of the paleontologists, evolutionary biologists, and ecologists who gathered for the colloquium would consider themselves first and foremost conservation biologists, and most of the invited speakers built their
careers on firm foundations of basic research. Yet they seemed united by the concern that human disturbance of the world's ecosystems threatens not just the persistence of particular species and communities, but the integrity of the very evolutionary processes they have spent their careers studying. The loss of biodiversity and its ramifications on evolution "is far and away the biggest issue of our time, by a long long way," conference organizer Norman Myers of Oxford University said in kicking off the meeting - and many participants seemed to agree.
The colloquium departed from orthodoxy in several respects. Explicit attention was given to conservation issues, and informal discussions outweighed formal presentations. In addition, Myers and co-organizer Andrew Knoll of Harvard University urged scientists to engage in unbridled speculation about future trends and outcomes; this participants did with some restraint. Finally, although the conference aimed to address scientific questions to an audience of scientists, discussion repeatedly shifted to the subject of communicating with the public and with policy makers. On issue after issue, debate returned to whether and how scientists should educate and influence society in order to effect change.
|Is there a silver lining to mass extinctions?
The meeting began from the paleontological perspective, addressing the nature of past extinction events and what lessons might be learned from them. Is the present anthropogenic extinction event fundamentally different from previous ones? Are we yet to the point where we can term today's event a mass extinction? By depleting numerous species, are we also degrading ecosystem function? Are we imperiling the ability of evolution to bounce back? If mass extinctions promote biotic homogenization by small numbers of surviving taxa, is this analogous to present-day invasions of exotic species (as we enter the "Homogocene")? And, is there a silver lining to mass extinctions - do they open up niches, inducing a rapid round of adaptive radiation by survivors? Or do they, instead, deplete so many species that - if niches are created by organisms - recovery is very slow?
After a mass extinction, the biota does not bounce back rapidly. The fossil record tells us there's a substantial lag time and that following an extinction event there is, in fact, further loss of
surviving groups by slow attrition. David Jablonski of the University of Chicago presented evidence for this, terming these doomed taxa "dead clades walking." Some meeting participants declared that today's extinction event is closing off more diversifying opportunities than it's opening, although others argued the question is still in play. All agreed, however, that if a silver lining of post-extinction speciation exists, it occurs in a time frame beyond which we'd be able to appreciate it. Even a (brief) five-million-year recovery would comprise 15 or 20 times the duration that humans have existed as a species. So, if the world's biodiversity were to recover in a few million years, but we aren't around to see it, then maybe conservation arguments really are about human concerns, not those of the nonhuman world, which may go on as always, long after we're gone.
|Smaller extinction events have lessons, too.
All participants agreed that more paleontological research needs to be focused on periods
of recovery from extinction events. And many agreed with Jablonski that while history's "big five" mass extinctions
get a lot of attention, scientists should shift their focus to smaller extinction events and to
times of low extinction intensities (in which over 95 percent of all species have disappeared). Analogous
to this on the conservation front is that we may pay too much attention to dramatic, obvious
disturbances like habitat loss, whereas slow, inexorable deterioration of populations, communities,
and ecosystems might pose a larger long-term threat.
|"National parks are doomed."
As the meeting progressed through neontological studies and syntheses, consensus emerged that in a world increasingly dominated by humans, evolutionary biology could benefit by shifting its research focus away from allegedly pristine systems and toward study of human-disturbed ones. As for conservation
policy, participants suggested that it might best move toward incorporating people and their economic needs in its equations. In addition, preservation of biodiversity hot spots as the primary approach for preventing biological losses was questioned by those who pointed out that global climate change will reduce the effectiveness of preserves, if geographic ranges of species shift and local environments are modified. "National parks are doomed," said David Woodruff of the University of California at San Diego, summing up the conclusion of one working group. "They are static solutions to dynamic problems. We need to somehow extend them so organisms can adapt to climate change."
But how to accomplish such extension? Some participants argued for new approaches that incorporate conservation measures into human-inhabited areas
where landscape already has been extensively altered. Others argued that we should seek to preserve ecological and evolutionary processes (not just species and habitats) by making sure ecological gradients are protected and that phenomena such as natural fire regimes are maintained.
|"We need to push cultural evolution in the right direction."
At the meeting's dinner lecture, Stanford University biologist, author, and
conservation advocate Paul Ehrlich applauded the extension of concern about the world's biota past merely species and habitats, to natural processes. Ehrlich urged evolutionary biologists to think about the cultural evolution of our species and to promote conservation ethics to the public. "We need to push cultural evolution in the right direction," he said, "and get people to care."
While the gathering seemed hesitant to speculate too freely about future
trends, some general predictions were advanced. In addition to numerous species extinctions in coming decades and centuries, scientists concluded, we should expect:
- Loss of genetic diversity in the surviving species.
- Breakdown of ecological relationships, particularly mutualisms (like
pollination, which provides much of our food).
- Turnovers in community structure (many of which have already occurred).
- Effects of continued global warming, including:
(a) range-shrinking and extinction of organisms (long-lived trees, vertebrates) that can't evolve fast enough to adapt to climate change;
(b) spread and dominance of those that can (insects, bacteria, viruses; expect many more tropical diseases moving into the temperate zone);
(c) failure of the nature preserve strategy due to shifts in species ranges.
- Increase in species that thrive in human-dominated landscapes
(house sparrows, starlings, etc.).
- Biotic homogenization of the world via invasive species. As the
biological equivalents of Wal-Marts and McDonalds spread through the world, we will live in the "new Pangaea," and our children will inherit a world of pests and weeds.
- The beginnings of divergence of new species from the homogenizers. Groups seeing rapid speciation and dominance within the timescale of human experience will be the microbes (and the diseases they carry); larger species, such as vertebrates, will evolve too slowly.
|"As long as there's life, there's evolution."
But could evolution itself actually end? Such a view is nonsense, the group agreed. "We're never going to stop evolution. As long as there's life, there's evolution," said Alan Templeton of Washington University, St. Louis. "But evolutionary processes can be disrupted." Indeed, the idea that they may produce results fundamentally different from what we know in today's world is a notion increasingly supported by scientific data.
We're living in dynamic times, the scientists agreed, and while the massive alteration of Earth's biotic systems is worrisome and dangerous, it also opens up countless opportunities for evolutionary research. "From the standpoint of pure science," Myers said, "Charles Darwin would say this is
the most exciting time to be an evolutionary biologist." Woodruff agreed.
Not only is the application of evolutionary biology to conservation
questions extremely important to our future, he told the group, but it
"provides some of the best science to be done."